I totally agree. It is, however a flawed argument in the context of legalization. One of the arguments for the legalization by the health ministry is that prohibition has been ineffective, factually not avoiding or even reducing (excess) weed consumption (among minors). Prohibition has criminalized many people for their consumption (via necessary circumstances such as possession), at the same time often denying help to those consumers who needed it.
The goals of drug policy should be: - help consumers to avoid or treat harmful consumption, especially minors - do not criminalize adult citizens who do no harm to others
Neither of these goals have been achieved by prohibition. Legalization is not going to help on the first point either, but might make it easier.
In the context of the second point: prohibition has been a nasty vehicle for arbitrary, often racist policing. Given that prohibition is not realistically possible in full consequence, the inherent tools of criminalizing alleged drug users are often applied to specific groups only, often for racist motives. Throwing around cocaine at the company party of your startup will hardly be punished, whereas the immigrant neighbor ends up in jail for smoking a joint.